Inspection apparatus and inspection method

ABSTRACT

An inspection apparatus for inspecting an inspection target surface arranged on an inspection plane, includes an X-ray generation tube having a target including an X-ray generation portion that generates X-rays by irradiation with an electron beam, and configured to emit X-rays to the inspection plane; and an X-ray detector configured to detect X-rays emitted from a foreign substance existing on the inspection target surface irradiated with the X-rays from the X-ray generation portion and totally reflected by the inspection target surface. The X-ray detector has an energy resolution not less than 1 keV or the X-ray detector has no energy analysis function.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of International Patent ApplicationNo. PCT/JP2022/043908, filed on Nov. 29, 2022, which claims priority toand the benefit of Japanese Patent Application No. 2022-013653, filed onJan. 31, 2022, the entire disclosures of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an inspection apparatus and aninspection method.

Description of the Related Art

Japanese Patent Laid-Open No. 2009-236622 describes a high-resolutionX-ray microscope apparatus with an X-ray fluorescence analysis function,that includes a detector configured to detect fluorescent X-rays whichare generated from a sample by focusing electron beams on an X-raygeneration target by an object lens and irradiating the sample withX-rays generated from the target, and an analysis unit configured toanalyze the fluorescent X-rays from the detection result of thedetector. Japanese Patent Laid-Open No. 2009-236622 also describes anarrangement in which the whole detector or part of the detector isincorporated in the magnetic circuit of the object lens.

In recent years, for example, there has been a problem that a foreignsubstance having a size equal to or smaller than several tens of µm istaken into a product and causes a defect. For example, in a lithium ionbattery, with respect to a constituent member using carbon, copper, oraluminum as a material, a micronization of foreign substance ofstainless steel or part of the constituent member may be taken into thebattery at the time of manufacturing.

If, at the time of manufacturing a lithium ion battery, a foreignsubstance is taken into the battery, a separator for maintaininginsulation in the battery may break due to a vibration of the foreignsubstance after shipping of the battery. In this case, the battery maybe short-circuited and ignite or explode.

If a foreign substance can be detected nondestructively, it is possibleto prevent distribution of a product that may ignite or explode. As amethod of detecting a foreign substance existing on the surface of asample using X-rays and specifying the element of the foreign substance,there are provided X-ray Fluorescence (to also be called XRF) andGrazing Incidence X-ray Fluorescence (to also be called TXRF). In X-rayFluorescence, the element of a sample substrate is also excited. InGrazing Incidence X-ray Fluorescence, incident X-rays are scattered dueto a foreign substance. Therefore, in these measurement methods, thereis a problem that the intensity ratio of the generated fluorescentX-rays becomes low due to the foreign substance.

SUMMARY OF INVENTION

The present invention has as its object to provide a techniqueadvantageous in detecting a foreign substance existing on an inspectiontarget surface with high sensitivity.

A first aspect of the present invention provides an inspection apparatusfor inspecting an inspection target surface arranged on an inspectionplane, comprising: an X-ray generation tube having a target including anX-ray generation portion that generates X-rays by irradiation with anelectron beam, and configured to emit X-rays to the inspection plane;and an X-ray detector configured to detect X-rays emitted from a foreignsubstance existing on the inspection target surface irradiated with theX-rays from the X-ray generation portion and totally reflected by theinspection target surface, wherein the X-ray detector has an energyresolution not less than 1 keV or the X-ray detector has no energyanalysis function.

A second aspect of the present invention provides an inspection methodof inspecting an inspection target surface arranged on an inspectionplane, comprising: an X-ray detection step of emitting X-rays to theinspection plane and detecting, by an X-ray detector, X-rays emittedfrom a foreign substance existing on the inspection target surface andtotally reflected by the inspection target surface; and a processingstep of processing an output of the X-ray detector, wherein the X-raydetector has an energy resolution not less than 1 keV or the X-raydetector has no energy analysis function.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically showing the arrangement of an inspectionapparatus according to the first embodiment;

FIG. 2 is a view showing a practical example of the arrangement of theinspection apparatus according to the first embodiment;

FIG. 3 is a view schematically showing an example of the arrangement ofan X-ray generation tube;

FIG. 4 is an enlarged schematic view of part of the inspection apparatusshown in FIG. 2 ;

FIG. 5 is an enlarged schematic view of part of the inspection apparatusshown in FIG. 2 ;

FIG. 6 is a graph exemplifying the relationship between a distanceD_(xs) (abscissa) and the count (ordinate) of foreign substancesdetected by an X-ray detector;

FIG. 7 is a view showing a practical example of the arrangement of theinspection apparatus according to the embodiment;

FIG. 8 is a view schematically showing the arrangement of an inspectionapparatus according to the second embodiment;

FIG. 9 is a view schematically showing the arrangement of an inspectionapparatus according to the third embodiment; and

FIG. 10 is a view schematically showing the arrangement of an inspectionapparatus according to the fourth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe attached drawings. Note, the following embodiments are not intendedto limit the scope of the claimed invention. Multiple features aredescribed in the embodiments, but limitation is not made to an inventionthat requires all such features, and multiple such features may becombined as appropriate. Furthermore, in the attached drawings, the samereference numerals are given to the same or similar configurations, andredundant description thereof is omitted.

FIG. 1 schematically shows the arrangement of an inspection apparatus IAaccording to the first embodiment of the present disclosure. Theinspection apparatus IA can be formed as, for example, an inspectionapparatus that inspects an inspection target surface TS arranged on aninspection plane IP. The inspection plane IP is a plane on which theinspection target surface TS should be arranged, and the inspectiontarget surface TS is one surface of an inspection target object IT. Theinspection apparatus IA can include an X-ray generation tube 101. TheX-ray generation tube 101 has a target (not shown) including an X-raygeneration portion XG that generates X-rays by irradiation with anelectron beam, and emits X-rays XR to the inspection plane IP. A foreignsubstance FS irradiated with the X-rays XR from the X-ray generationportion XG generates X-rays corresponding to a material forming theforeign substance FS, and such X-rays are also called fluorescent X-raysor characteristic X-rays. Some of the X-rays generated by the foreignsubstance FS irradiated with the X-rays XR are totally reflected by theinspection target surface TS. The X-rays emitted from the foreignsubstance FS and totally reflected by the inspection target surface TSare represented as X-rays XF. The inspection apparatus IA can include anX-ray detector 120. The X-ray detector 120 can be configured to detectthe X-rays XF emitted from the foreign substance FS existing on theinspection target surface TS irradiated with the X-rays XR from theX-ray generation portion XG and totally reflected by the inspectiontarget surface TS. The inspection apparatus IA can further include aprocessor that performs processing of detecting the foreign substance FSbased on an output from the X-ray detector 120. The processor canfurther perform processing of specifying the material forming theforeign substance FS based on the output from the X-ray detector 120.The processor can be implemented by, for example, a controller thatcontrols the operation of the inspection apparatus IA.

FIG. 2 shows a practical example of the arrangement of the inspectionapparatus IA shown in FIG. 1 . The inspection apparatus IA can includean X-ray generation apparatus 100, the X-ray detector 120, and acontroller 140. The X-ray generation apparatus 100 can include the X-raygeneration tube 101 and a driving circuit 103 that drives the X-raygeneration tube 101. The X-ray generation apparatus 100 can furtherinclude a boosting circuit 102 that supplies a boosted voltage to thedriving circuit 103. The X-ray generation apparatus 100 can furtherinclude a storage container (not shown) that stores the X-ray generationtube 101, the driving circuit 103, and the boosting circuit 102, and thestorage container can be filled with an insulating fluid such asinsulating oil. The controller 140 can be configured to control theX-ray generation apparatus 100 and the X-ray detector 120. Thecontroller 140 can have the function of the above-described processor.More specifically, the controller 140 can perform processing ofdetecting the foreign substance FS based on the output from the X-raydetector 120. Furthermore, the controller 140 can perform processing ofspecifying the material forming the foreign substance FS based on theoutput from the X-ray detector 120. The controller 140 can be formed by,for example, a PLD (an abbreviation of Programmable Logic Device) suchas an FPGA (an abbreviation of Field Programmable Gate Array), an ASIC(an abbreviation of Application Specific Integrated Circuit), ageneral-purpose or dedicated computer installed with a program, or acombination of all or some of these components.

The inspection apparatus IA may further include an X-ray detection panel130 that detects X-rays emitted from the X-ray generation portion XG andtransmitted through the inspection target object IT having theinspection target surface TS. The controller 140 can be configured togenerate an image (a transmission image of the inspection target objectIT) of the X-rays transmitted through the inspection target object ITbased on an output from the X-ray detection panel 130 and detect theforeign substance FS existing on the inspection target surface TS basedon the image. It is possible to detect a foreign substance existinginside the inspection target object IT and a foreign substance existingon a surface on the opposite side of the inspection target surface TSusing the X-ray detection panel 130. The controller 140 can beconfigured to detect the existence of the foreign substance FS and alsodetect the position and/or size of the foreign substance FS. Byproviding the X-ray detection panel 130 in addition to the X-raydetector 120, the foreign substance FS that cannot be detected by theX-ray detector 120 can be detected by the X-ray detection panel 130,thereby making it possible to improve the accuracy of detection of theforeign substance FS. As compared with a system including twoapparatuses that acquire a transmission image and detect a foreignsubstance, respectively, the inspection apparatus IA that acquires atransmission image and detects a foreign substance using X-rays emittedfrom one X-ray generation tube is advantageous in reducing the size andthe cost.

The inspection apparatus IA may further include a display 150, and thecontroller 140 can be configured to display, on the display 150,information indicating the constituent material of the foreign substanceFS specified based on the output from the X-ray detector 120. Thecontroller 140 can further be configured to display, on the display 150,the transmission image of the inspection target object IT generatedbased on the output from the X-ray detection panel 130. In addition, thecontroller 140 can be configured to display, on the display 150,information indicating the position and/or size of the foreign substancedetected based on the output from the X-ray detection panel 130. Thecontroller 140 may be formed by a single unit or may be divided into aplurality of units.

FIG. 3 schematically shows an example of the arrangement of the X-raygeneration tube 101. The X-ray generation tube 101 can include anelectron gun EG, an anode 93 having a target 933 including the X-raygeneration portion XG that generates X-rays when electrons from theelectron gun EG collide, and an insulating tube 92. In the X-raygeneration tube 101, the anode 93 can be arranged to close one of thetwo opening ends of the insulating tube 92, and a closing member 91including the electron gun EG can be arranged to close the other of thetwo opening ends of the insulating tube 92. A deflector 94 that deflectsthe flow (electron beam) of electrons from the electron gun EG may bearranged outside the insulating tube 92. The X-ray generation tube 101shown in FIG. 3 is an example of a sealed transmission type X-raygeneration tube in which the internal space of the insulating tube 92 ismaintained in a vacuum state and X-rays are transmitted through thetarget 933 and a target holding plate 932 (to be described later).However, as the X-ray generation tube 101, an unsealed open type ornon-transmission reflection type X-ray generation tube may be adopted.

The deflector 94 can be arranged outside the X-ray generation tube 101.With respect to a direction parallel to an axis AX of the X-raygeneration tube 101, the deflector 94 can be provided between the anode93 and a cathode (not shown). In an example, with respect to thedirection parallel to the axis AX of the X-ray generation tube 101, thedeflector 94 is provided between the electron gun EG and the target 933.More specifically, a virtual plane 97 crossing the deflector 94 can belocated in a space sandwiched between a virtual plane 95 contacting thedistal end of the electron gun EG and a virtual plane 96 contacting partof the target 933. The virtual planes 95, 96, and 97 are planesorthogonal to the axis AX of the X-ray generation tube 101.

The anode 93 can include the target 933, the target holding plate 932that holds the target 933, and an electrode 931 that holds the targetholding plate 932. The electrode 931 is electrically connected to thetarget 933 and can give a potential to the target 933. The target 933generates X-rays when electrons (electron beam) emitted from theelectron gun EG collide against the target 933. The X-ray generationportion XG is a portion of the surface of the target 933, against whichthe electrons (electron beam) collide. The X-rays generated by the X-raygeneration portion XG are transmitted through the target holding plate932 and emitted to the outside of the X-ray generation tube 101. Theanode 93 can be maintained at, for example, the ground potential but maybe maintained at another potential.

The target 933 is made of a metal material. The target 933 is desirablymade of a material having a high melting point, for example, tungsten,tantalum, molybdenum, or the like, which contributes to improvement ofX-ray generation efficiency. The target holding plate 932 can be made ofa material that readily passes X-rays, for example, beryllium, diamond,or the like. The target holding plate 932 is desirably made of diamond.This can decrease the thickness of the target holding plate 932 whilemaintaining the strength of the target holding plate 932, and candecrease the distance between the inspection plane IP (inspection targetsurface TS) and the target 933 (X-ray generation portion XG). Thethickness of the target holding plate 932 is desirably thin. Morespecifically, the thickness of the target holding plate 932 is desirably4 mm or less, and more desirably 2 mm or less, 1 mm or less, or 0.3 mmor less. The thickness of the target holding plate 932 can be set withreference to the distance from the X-ray generation portion XG to theinspection plane IP, which is necessary to specify an element containedin the foreign substance (to be described later). To specify the elementcontained in the foreign substance, the target holding plate 932 isdesirably, extremely thin. However, the target holding plate 932 isdesirably thick in terms of the processing cost and the individualdifference of the target holding plate 932, strength for maintaining theinternal space of the insulating tube 92 in the vacuum state, and thelike. Therefore, the optimum thickness of the target holding plate 932is desirably used. Note that FIG. 3 is not intended to show therelationship between the thickness of the target 933 and that of thetarget holding plate 932. For example, the thickness of the target 933may be several µm, and the thickness of the target holding plate 932 maybe several hundred µm.

FIG. 4 is an enlarged schematic view of part of the inspection apparatusIA shown in FIG. 2 . The foreign substance FS can exist on theinspection target surface TS. The X-rays (characteristic X-rays) XF thatare emitted from the foreign substance FS so as to be totally reflectedby the inspection target surface TS and are totally reflected by theinspection target surface TS enter an X-ray receiving portion 121 of theX-ray detector 120. On the other hand, fluorescent X-rays that can begenerated from the inspection target object IT by irradiation with theX-rays XR from the X-ray generation portion XG hardly enter the X-rayreceiving portion 121 of the X-ray detector 120 arranged to detect theX-rays (characteristic X-rays) XF. Therefore, the ratio of thefluorescent X-rays emitted from the inspection target object IT anddetected by the X-ray detector 120 with respect to the X-rays(characteristic X-rays) XF emitted from the foreign substance FS anddetected by the X-ray detector 120 can be made extremely low.

The X-ray detector 120 may be a silicon drift detector (SDD), a CdTedetector, or a CdZnTe detector. The X-ray detector 120 may be an energydispersion detector. If the X-ray detector 120 is an energy dispersiondetector, the controller (or processor) 140 can decide the material orelement forming the foreign substance FS based on the elemental profileof energy dispersion (a count value for each energy). Commercialsoftware may be installed on the controller (or processor) 140 to decidethe material or element forming the foreign substance FS. Examples ofsuch software are, for example, “XRS-FP Quantitative XRF AnalysisSoftware” of AMETEK or UniQuant software.

The specifications of the X-ray detector 120 can be decided inaccordance with an energy resolution necessary to detect a foreignsubstance. An example of a detector having a low energy resolution canbe a detector using a scintillator, an Si PIN photodiode, or a CCD. Anexample of a detector having an even higher energy resolution can be adetector using a proportional counter. An example of a detector havingan even higher energy resolution can be a detector applied with a CdTedirect-bandgap crystal or an energy dispersion detection method like anSi drift detector. An example of a detector having an even higher energyresolution can be a detector applied with a wavelength dispersiondetection method of obtaining energy from an angle using an analyzingcrystal.

To totally reflect, by the inspection target surface TS, the fluorescentX-rays from the foreign substance FS, an angle at which the fluorescentX-rays from the foreign substance FS enter the inspection target surfaceTS needs to be a total reflection critical angle θ_(c) or less.

$\begin{matrix}\begin{array}{l}{\delta = \left( \frac{r_{e}\lambda^{2}}{2\pi} \right)N_{0}\rho{\sum\limits_{i}{x_{i}\left( {z_{i} + f'_{i}} \right)/{\sum\limits_{i}{x_{i}M_{i}}}}}} \\{\theta_{c} \approx \sqrt{2\delta}}\end{array} & \text{­­­(1)}\end{matrix}$

-   θ_(c): total reflection critical angle-   r_(e): classical electron radius (2.818 × 10⁻¹⁵ m)-   N₀: Avogadro number-   λ: X-ray wavelength-   ρ: density (g/cm³)-   Zi, Mi, xi: atomic number, atomic weight, and atomic ratio (molar    ratio) of ith atom-   f′_(i): atomic scattering factor (anomalous dispersion term) of ith    atom

If the inspection target surface TS is made of a metal, the totalreflection critical angle is theoretically about 1° or less. However, infact, the metal surface is often oxidized or carbonized, or a reflectioncritical angle different from the theoretical value is often obtainedbecause, for example, the surface is covered with a graphite layer. If atotal reflection condition is satisfied when the inspection targetsurface TS is irradiated with the X-rays XR, an angle (total reflectioncritical angle) formed by the inspection target surface TS and thecharacteristic X-rays XF emitted from the foreign substance FS andtotally reflected by the inspection target surface TS is confirmed to be5° or less through an experiment. At this time, since the foreignsubstance FS is extremely small as compared with a distance D_(xs)between the X-ray generation portion XG and the inspection plane IP(inspection target surface TS), a position at which the X-rays emittedfrom the foreign substance FS are totally reflected by the inspectiontarget surface TS may be regarded as a position at which the X-rays XRfrom the X-ray generation portion XG enter the inspection plane IP. Ifthe foreign substance FS exists at a position where the X-rays XR fromthe X-ray generation portion XG vertically enter the inspection planeIP, as shown in FIG. 4 , the position at which the X-rays emitted fromthe foreign substance FS are totally reflected by the inspection targetsurface TS may be regarded as the position at which the X-rays XR fromthe X-ray generation portion XG vertically enter the inspection planeIP.

Since the total reflection critical angle is 5° or less, an angle θformed by the inspection plane IP and a virtual line connecting theX-ray receiving portion 121 of the X-ray detector 120 and the positionat which the X-rays XR from the X-ray generation portion XG enter theinspection plane IP can be set to 5° or less, desirably 2° or less, andmore desirably 1° or less. As the angle θ is smaller, the ratio of thefluorescent X-rays emitted from the inspection target object IT anddetected by the X-ray detector 120 with respect to the X-rays(characteristic X-rays) XF emitted from the foreign substance FS anddetected by the X-ray detector 120 can be made lower.

The X-ray detector 120 can be arranged at a position where the extensionplane of the inspection plane IP crosses the X-ray detector 120. Asschematically shown in FIG. 5 , the X-ray receiving portion 121 caninclude a window portion 122 that passes the X-rays XF. The windowportion 122 can have, for example, a diameter of several mm and athickness of several hundred µm. The window portion 122 can be made of,for example, beryllium. As schematically shown in FIG. 5 , theinspection apparatus IA may include a slit member 125 having a slit(opening) on a virtual line connecting the X-ray receiving portion 121of the X-ray detector 120 and the position at which the X-rays XR fromthe X-ray generation portion XG enter the inspection plane IP.

The size of the slit provided in the slit member 125 and the arrangementposition of the X-ray detector 120 can be decided in accordance with arange irradiated with the X-rays XR on the inspection target surface TS,the materials that can form the inspection target surface TS and theforeign substance FS, and the like. Consider a case in which foreignsubstances FS1 and FS3 exist at two ends of a width Y irradiated withthe X-rays XR on the inspection target surface TS, and a distance Z fromthe center of the width Y to the X-ray receiving portion 121 has thesame length as that of the width Y, as schematically shown in FIG. 7 .In this case, by setting the lower limit of a width W_(s) of the slit toY × tanθ, and setting a distance X₂ between the center of the X-rayreceiving portion 121 and the inspection plane IP to Y × tanθ, it ispossible to detect all foreign substances within the range irradiatedwith the X-rays XR on the inspection target surface TS.

To increase the intensity of the X-rays XF detected by the X-raydetector 120, the distance D_(xs) from the X-ray generation portion XGto the inspection plane IP is desirably made small. FIG. 6 shows aresult of obtaining, by an experiment, the relationship between thedistance D_(xs) (abscissa) and the count (ordinate) of foreignsubstances FS detected by the X-ray detector 120. The count is a totalcount (peak count), per predetermined time, of energy corresponding tothe position of fluorescent X-rays (for example, Ni Kα-rays) exitingfrom a specific element contained in the foreign substance. Consideringa count TH necessary to specify the element, the distance D_(xs) fromthe X-ray generation portion XG to the inspection plane IP is desirably5 mm or less, more desirably 4 mm or less, and still more desirably 3 mmor less. As the X-ray generation tube 101, for example, a sealedtransmission microfocus X-ray source of Canon ANELVA, more specifically,the G series, and still more specifically, the G-511 series or G-311series is useful.

To detect, by a transmission image, a foreign substance having a size ofseveral µm to several tens of µm with high sensitivity, a distanceD_(sf) from the inspection plane IP to the X-ray detection panel 130needs to be made sufficiently larger than D_(xs). For example, if 10pixels are necessary to detect a foreign substance having a diameter of5 µm, when an X-ray detection panel (FPD) having a pixel pitch of 100 µmis used, a magnification ratio of 100 × 10/5 = 200 is required fordetection. As for a foreign substance having a diameter of 50 µm, amagnification ratio of 20 is required for detection. Therefore,D_(sf)/D_(xs) is set to desirably 20 or more, and more desirably 200 ormore. This can detect a foreign substance with high sensitivity using atransmission image.

The inspection apparatus IA is useful to detect a foreign substanceattached to a material of a lithium ion battery in a manufacturing stepof the lithium ion battery, but is merely an example and is also usefulfor other application purposes. For example, the inspection apparatus IAmay be used to measure and analyze airborne particles such as PM2.5influencing the environment and health. In this case, by using theinspection apparatus IA for the conventional technique of periodically(for example, every hour or every day) measuring the number of particlesand the sizes of the particles, it is possible to simultaneously specifymaterials or elements forming the particles in addition to measurementof the number of particles and the sizes of the particles, therebyimplementing more advanced environmental and health measures.Alternatively, by using the inspection apparatus IA for the field ofsemiconductors, micronization of which has recently been advanced, suchas an “EUV mask manufacturing apparatus, an inspection apparatus, and aninspection apparatus of a semiconductor manufacturing step, it ispossible to improve a yield and early solve the cause of an abnormalityusing the element information of a foreign substance.

An inspection method of inspecting the inspection target surface TSarranged on the inspection plane IP using the inspection apparatus IAwill be described below. The inspection method can include an X-raydetection step of emitting X-rays to the inspection plane IP (inspectiontarget surface TS) and detecting, by the X-ray detector 120, the X-raysXF emitted from the foreign substance FS existing on the inspectiontarget surface TS and totally reflected by the inspection target surfaceTS, and a processing step of processing an output of the X-ray detector120. The processing step can include a step of detecting the foreignsubstance FS and/or a step of specifying a material forming the foreignsubstance FS. The inspection method can further include a step ofdetecting, by the X-ray detection panel 130, X-rays transmitted throughthe inspection target object IT having the inspection target surface TS,and in the processing step, the output of the X-ray detector 120 and anoutput of the X-ray detection panel 130 can be processed. The processingstep can include a step of detecting the existence of the foreignsubstance FS and the position of the foreign substance FS based on theoutput of the X-ray detection panel 130. Alternatively, the processingstep can include a step of detecting the existence of the foreignsubstance FS, the position of the foreign substance FS, and the size ofthe foreign substance FS based on the output of the X-ray detectionpanel 130.

In the first embodiment, the inspection apparatus having the function ofspecifying a material forming a foreign substance has been explained.However, the inspection apparatus need not have the function ofspecifying a material forming a foreign substance. For example, in acase where an inspection speed is improved or a case where a movinginspection target object is inspected, a limited amount of X-raysemitted from a foreign substance and totally reflected can be detected.Therefore, sufficient foreign substance specifying accuracy cannot beobtained, and a foreign substance on the inspection target object ismissed, thereby lowering the manufacturing yield. However, it ispossible to implement high-speed inspection by forming an inspectionapparatus that detects only the presence/absence of a foreign substancewithout specifying a material forming a foreign substance. In addition,there can be provided an inexpensive inspection apparatus by eliminatinga function of specifying the position of a foreign substance by an imageof X-rays transmitted through an inspection target object. Furthermore,if the function of specifying a material forming a foreign substance isunnecessary, it is possible to use an inexpensive X-ray detector (forexample, a proportional counter or NaI scintillator) having a low energyresolution of 1 keV or more (a coarse resolution with a large half-valuewidth of given intensity). In addition, an inexpensive X-ray detectorthat has a high energy resolution of about several eV but has no energyanalysis function, represented by PIN and CCD photodiodes, can be used.These inexpensive X-ray detectors have high detection efficiency oflow-energy X-rays (50 eV to 50 keV). Thus, the X-ray detector 120 can bean X-ray detector that detects X-rays having energy within a range of 50eV to 50 keV.

To detect X-rays emitted from a foreign substance by irradiation withX-rays from one X-ray generation apparatus and totally reflected, aplurality of detectors may be provided. By providing a plurality ofdetectors, it is possible to improve accuracy of detecting X-raysemitted from a foreign substance and totally reflected.

FIG. 8 schematically shows the arrangement of an inspection apparatus IAaccording to the second embodiment. Matters not mentioned in the secondembodiment can comply with the first embodiment. The inspectionapparatus IA according to the second embodiment can include a pluralityof X-ray detectors, for example, a first X-ray detector 1201 and asecond X-ray detector 1202. The first X-ray detector 1201 and the secondX-ray detector 1202 can be arranged to face each other via an axis AX ofan X-ray generation tube 101. From another viewpoint, the first X-raydetector 1201 and the second X-ray detector 1202 can be arranged to faceeach other. Each of the first X-ray detector 1201 and the second X-raydetector 1202 can be formed by an inexpensive X-ray detector such as aPIN photodiode. The inspection apparatus IA according to the secondembodiment can include slit members 1251 and 1252 similar to the slitmember 125 in the inspection apparatus IA of the first embodiment. Theslit members 1251 and 1252 are can be provided for the first X-raydetector 1201 and the second X-ray detector 1202, respectively. Aforeign substance FS1 irradiated with X-rays XR from an X-ray generationportion XG emits X-rays radially (for example, in all directions of360°), and some of the X-rays can totally be reflected by an inspectiontarget surface TS. The X-rays totally reflected by the inspection targetsurface TS include, for example, X-rays XF11 entering the first X-raydetector 1201 and X-rays XF12 entering the second X-ray detector 1202.The X-rays XF11 and XF12 shown in FIG. 8 can be understood as trajectoryvectors of X-ray photons. Another foreign substance can exist on theinspection target surface TS in addition to the foreign substance FS1.Therefore, the X-rays emitted from the foreign substance FS1 and totallyreflected by the inspection target surface TS may be blocked by theother foreign substance and may not enter one of the plurality of X-raydetectors. However, by arranging the plurality of X-ray detectors, thepossibility that one of the plurality of X-ray detectors can detect theX-rays emitted from the foreign substance FS1 and totally reflected bythe inspection target surface TS becomes higher.

FIG. 9 schematically shows the arrangement of an inspection apparatus IAaccording to the third embodiment. FIG. 9 is a view of the inspectionapparatus IA when viewed from an oblique direction. Matters notmentioned in the third embodiment can comply with the first or secondembodiment. FIG. 9 does not illustrate a slit member but a slit membermay be provided, similar to the second embodiment. The inspectionapparatus IA can include a conveyance mechanism CV that conveys aninspection target object IT along a conveyance direction DIR.

A first X-ray detector 1201 and a second X-ray detector 1202 can bearranged at positions apart from each other in a direction parallel tothe conveyance direction DIR or a direction parallel to the longitudinaldirection of the inspection target object IT. FIG. 9 shows X-rays XF11(a trajectory vector of X-ray photons) and X-rays XF12 (a traj ectoryvector of X-ray photons) emitted from a foreign substance FS1 irradiatedwith X-rays XR from an X-ray generation portion XG and totally reflectedby an inspection target surface TS. The X-rays XF11 enter the firstX-ray detector 1201 and the X-rays XF12 enter the second X-ray detector1202.

A foreign substance FS2 different from the foreign substance FS1 canexist on the inspection target surface TS. In the example shown in FIG.9 , the foreign substance FS2 exists between the foreign substance FS1and the first X-ray detector 1201. If the X-rays XF11 are blocked by theforeign substance FS2, the first X-ray detector 1201 cannot detect theX-rays XF11. However, the second X-ray detector 1202 can detect theX-rays XF12 from the foreign substance FS1. This can reduce thepossibility that the foreign substance on the inspection target surfaceTS of the inspection target object IT is missed, thereby preventing themanufacturing yield from lowering. Furthermore, based on the positionalrelationship between the second X-ray detector 1202 that has detectedthe foreign substance and the first X-ray detector 1201 that cannotdetect the foreign substance, the position of the foreign substance canbe estimated. For example, in the example shown in FIG. 9 , it can beestimated that the foreign substance FS2 exists between the foreignsubstance FS1 and the second X-ray detector 1202.

The inspection apparatus IA may include an additional X-ray detectorthat is arranged to detect X-rays totally reflected by a foreignsubstance existing on a surface on the opposite side of the inspectiontarget surface TS.

FIG. 10 schematically shows the arrangement of an inspection apparatusIA according to the fourth embodiment. Matters not mentioned in thefourth embodiment can comply with the first to third embodiments. FIG.10 shows X-rays XF11 and XF12 emitted from a foreign substance FS1 andtotally reflected by an inspection target surface TS. The inspectionapparatus IA according to the fourth embodiment can include an X-raydetector 1205 including a long X-ray receiving portion 1206 that extendsin a predetermined direction. The X-ray detector 1205 can be formed byan inexpensive X-ray detector such as a PIN photodiode. In the exampleshown in FIG. 10 , the X-ray receiving portion 1206 extends in adirection parallel to a surface parallel to the inspection targetsurface TS. From another viewpoint, the X-ray receiving portion 1206extends in a direction parallel to the longitudinal direction of theinspection target object IT. From still another viewpoint, the X-rayreceiving portion 1206 extends in a direction parallel to a conveyancedirection DIR. The X-ray receiving portion 1206 can have a rectangularshape having short and long sides, and the longitudinal direction is adirection parallel to the long side. The long side can have, forexample, a length which is three or more times longer than the shortside.

Although not shown in FIG. 10 , the inspection apparatus IA may includea slit member having a slit, and the slit member can have a rectangularshape that extends along the longitudinal direction of the X-rayreceiving portion 1206. The slit may be divided into a plurality ofpartial slits and then arranged. The slit member is advantageous inimproving the detection accuracy of a foreign substance. Furthermore, byproviding the slit member, it is possible to specify the position of aforeign substance based on the positional relationship between the X-rayreceiving portion 1206 and the slit.

The long X-ray receiving portion 1206 is advantageous in detecting theforeign substance FS1 even in a case where some of the X-rays emittedfrom the foreign substance FS1 and totally reflected by the inspectiontarget surface TS are blocked by another foreign substance FS2. In theexample shown in FIG. 10 , the X-rays XF11 emitted from the foreignsubstance FS1 and totally reflected by the inspection target surface TScan be blocked by the foreign substance FS2 but the X-rays XF12 emittedfrom the foreign substance FS1 and totally reflected by the inspectiontarget surface TS can enter the X-ray receiving portion 1206. Theinspection apparatus IA may include two or more X-ray detectors 1205.The two or more X-ray detectors 1205 can be arranged so that thelongitudinal directions coincide with directions parallel to theconveyance direction DIR. In addition, the two or more X-ray detectors1205 can be arranged to overlap each other in a direction orthogonal tothe conveyance direction DIR. The inspection apparatus IA may furtherinclude an X-ray detector including an X-ray receiving portion with alongitudinal direction extending along a direction intersecting theconveyance direction DIR, for example, a direction orthogonal to theconveyance direction DIR.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention, the following claims are made.

1. An inspection apparatus for inspecting an inspection target surfacearranged on an inspection plane, comprising: an X-ray generation tubehaving a target including an X-ray generation portion that generatesX-rays by irradiation with an electron beam, and configured to emitX-rays to the inspection plane; and an X-ray detector configured todetect X-rays emitted from a foreign substance existing on theinspection target surface irradiated with the X-rays from the X-raygeneration portion and totally reflected by the inspection targetsurface, wherein the X-ray detector has an energy resolution not lessthan 1 keV or the X-ray detector has no energy analysis function.
 2. Theinspection apparatus according to claim 1, further comprising aprocessor configured to perform processing of detecting the foreignsubstance based on an output of the X-ray detector.
 3. The inspectionapparatus according to claim 1, wherein the X-ray detector can detectX-rays having energy within a range of 50 eV to 50 keV.
 4. Theinspection apparatus according to claim 1, wherein a distance betweenthe inspection plane and the X-ray generation portion is not larger than5 mm.
 5. The inspection apparatus according to claim 1, wherein adistance between the inspection plane and the X-ray generation portionis not larger than 3 mm.
 6. The inspection apparatus according to claim1, wherein an angle formed by the inspection plane and a virtual lineconnecting an X-ray receiving portion of the X-ray detector and aposition at which the X-rays from the X-ray generation portion enter theinspection plane is not larger than 5°.
 7. The inspection apparatusaccording to claim 1, wherein an angle formed by the inspection planeand a virtual line connecting an X-ray receiving portion of the X-raydetector and a position at which the X-rays from the X-ray generationportion enter the inspection plane is not larger than 2°.
 8. Theinspection apparatus according to claim 6, further comprising a slitmember having a slit on the virtual line.
 9. The inspection apparatusaccording to claim 1, further comprising an X-ray detection panelconfigured to detect X-rays emitted from the X-ray generation portionand transmitted through an inspection target object having theinspection target surface.
 10. The inspection apparatus according toclaim 1, wherein the X-ray generation tube is of a sealed transmissiontype.
 11. The inspection apparatus according to claim 1, wherein t theX-ray generation tube includes a target holding plate configured to holdthe target, and a thickness of the target holding plate is not largerthan 4 mm.
 12. The inspection apparatus according to claim 11, whereinthe target holding plate contains diamond.
 13. The inspection apparatusaccording to claim 1, further comprising a conveyance mechanismconfigured to convey an inspection target object having the inspectiontarget surface.
 14. The inspection apparatus according to claim 13,further comprising, in addition to the X-ray detector, at least oneX-ray detector configured to detect the X-rays emitted from the foreignsubstance existing on the inspection target surface irradiated with theX-rays from the X-ray generation portion and totally reflected by theinspection target surface.
 15. The inspection apparatus according toclaim 14, wherein the X-ray detector and the at least one X-ray detectorare arranged apart from each other in a direction parallel to aconveyance direction of the inspection target object by the conveyancemechanism.
 16. The inspection apparatus according to claim 13, whereinthe X-ray detector includes a long X-ray receiving portion.
 17. Theinspection apparatus according to claim 16, wherein a longitudinaldirection of the X-ray receiving portion is parallel to a directionparallel to a conveyance direction of the inspection target object bythe conveyance mechanism.
 18. An inspection method of inspecting aninspection target surface arranged on an inspection plane, comprising:an X-ray detection step of emitting X-rays to the inspection plane anddetecting, by an X-ray detector, X-rays emitted from a foreign substanceexisting on the inspection target surface and totally reflected by theinspection target surface; and a processing step of processing an outputof the X-ray detector, wherein the X-ray detector has an energyresolution not less than 1 keV or the X-ray detector has no energyanalysis function.
 19. The inspection method according to claim 18,wherein the processing step includes a step of detecting the foreignsubstance.
 20. The inspection method according to claim 18, wherein theX-ray detector can detect X-rays having energy within a range of 50 eVto 50 keV.